For the purpose of generating a pn junction for use in the fabrication of a light emitting diode, ZnO is an excellent material having n-type characteristics, which generates near UV light, at about 380 nm. A corresponding p-type material is required to complete the pn structure. Currently, candidate p-type materials include Cu(I) based oxides, such as SrCu2O2, AlCuO2 and GaCuO2. In 2002, Ohta et al., Fabrication and Current Injection UV-light Emission from a transparent p-n Heterojunction Composed of p-SrCu2O2 and n-ZnO, Key Engineering Materials, Vol. 214–215 (2002) pp. 75–80, reported the fabrication of pn heterojunctions of p-SrCu2O2 and n-ZnO, using a pulsed laser ablation deposition technique. The integration of films includes single crystal yittria-stabilized zirconia ZrO2 (YSZ) as the substrate, indium-tin-oxide (ITO) as a transparent n-type electrode, and the combination of n-type ZnO and p-type SrCu2O2 for the pn junction, and a thin nickel film as the top electrode. From this structure, electroluminescence was observed.
Also in 2002, Martinson, Synthesis of Single Phase SrCu2O2 from liquid precursors, Journal of Young Investigators, Vol. 10. Issue 3, March 2004, reported the synthesis of single phase SrCu2O2 from water based liquid precursors using a spray technique, however, there is no mention of the integration of n-type ZnO and p-SrCu2O2 in this publication.
To our knowledge, there are no reports on the preparation of a strong p-type calcium-doped SrCu2O2 thin film via spin-coating process. Nie et al., First-principles study of transparent p-type conductive SrCu2O2 and related compounds, Physical Review B, Vol. 65, 2002, pp 075111, reported theoretical studies on the electrical properties of [Sr1-xCax]Cu2O2, and stated that they expected the best p-type properties for compositions where x=0.16. There were no experimental data to support their studies.
In our prior filed patent application Ser. No. 11/220,885, filed Sep. 6, 2005, for Method of SrCu2O2 spin-on precursor synthesis and low temperature p-type thin film deposition, we disclosed a stable spin-on precursor. This work describes a stable, spin-on precursor having a calcium acetate component which provides for a higher quality thin film forming a pn junction.